In the past, many fastening members for vehicles plated with zinc on which black chromate films were formed by using hexavalent chromium were used because of their inexpensiveness, high corrosion preventive effect, and good design. However, with the recent environmental restriction on hexavalent chromium, fastening members for vehicles on which black chemical conversion films are formed by using trivalent chromium as an alternative to hexavalent chromium have been used. When, however, trivalent chromium is used, the corrosion resistance, the scratch resistance, and the black appearance of the member are not stable, which makes it difficult to stably obtain high-quality black members. Especially when a trivalent chromium black chemical conversion treatment liquid is used continuously, zinc is accumulated in the treatment liquid. If the zinc concentration exceeds 10 g/L, it is difficult to manage the liquid for obtaining a good appearance and a good corrosion resistance, and hence it is difficult to stably obtain high-quality members. Moreover, if the zinc concentration exceeds 15 g/L, it is not possible to obtain members having a good black appearance and a high corrosion resistance. For this reason, it is necessary to frequently exchange the treatment liquid, which presents a problem of great increase in costs.